Most human beings experience peak physical performance in their late teens and begin a slow decline in their early 20s, whose course is greatly affected by the activity levels undertaken by individuals in the years that follow. Many studies provide evidence that in developed nations such as the U.S., a sedentary lifestyle contributes significantly to development of the major risk factors for age-related disease, prominent among them obesity, diabetes, and hypertension. Conversely, numerous studies document the benefits of physical activity, and in particular structured exercise programs, not only for reducing disease risk and improving physical performance, but also for enhancing substantially the quality of daily life. Aerobic and resistance training have complementary benefits, and can be undertaken at almost any age and physical condition, given appropriate medical clearance and supervision as warranted.